Digital relay

Abstract

The invention includes an output circuit that outputs an operation signal to a direct current breaker that interrupts a direct current main circuit, and a processor that samples, at predetermined time intervals, digital data wherein a value detected by a direct current transformer that detects a current of the direct current main circuit is measured as an input current, calculates a computed measurement value to be output to a display circuit, and outputs control information for executing a protection process using measurement value sampling data obtained by the sampling to the output circuit, and executes a protection process of the direct current main circuit at every sampling.

The invention claimed is: 
     
       1. A digital relay that protects a direct current power system, the digital relay comprising:
 a measurement circuit that measures, as an input current, a value detected by a current detecting device that detects a current flowing in the power system, and outputs the measured value as digital data; 
 an output circuit that outputs an operation signal to a switching device that interrupts the power system; 
 a display circuit that outputs a display signal to display means; and 
 a processor that outputs a display signal to the display circuit based on the digital data, and outputs control information to the output circuit, wherein 
 the processor samples the digital data at predetermined time intervals and, in addition to performing a measurement process for output to the display circuit, outputs control information for executing a protection process using sampling data obtained by the sampling to the output circuit, and executes the protection process of the power system, and 
 wherein the protection process comprises a high speed protection process that needs high speed and a normal protection process that does not need high speed, and the high speed protection process is executed every one sampling, in addition to which the normal protection process is executed at a timing of one cycle in which N times' worth of sampling data are accumulated, with N as an integer of 2 or greater, and the measurement process is performed only at a timing at which M cycles elapse, with M as an integer of 2 or greater. 
 
     
     
       2. The digital relay of  claim 1 , wherein a computed value as a result of the measurement process is a power value or an average measurement value. 
     
     
       3. The digital relay of  claim 1 , wherein the high speed protection process comprises an overcurrent protection process or an overvoltage protection process, and wherein the normal speed protection process comprises an undercurrent protection process or a leakage current protection process. 
     
     
       4. The digital relay of  claim 1 , wherein the normal protection process is executed at least partially concurrently with the measurement process.